The invention relates generally to digital communication systems and in particular to local area network hardward protocols for digital communications.
As digital communication networks become more complex and sophisticated, many communication protocols have evolved. For example, in a token passing methodology, a node must wait until receipt and thus possession of the token or marker to transmit its data. Similarly, with respect to a polling protocol, each node is "time-slotted" access periods and must wait until it is polled. Furthermore, there exist what are called carrier wave crash detectors wherein a node attempts to reacquire the bus randomly. In each case bus access is allotted to the various nodes without regard to the relative urgency or priority of the messages.
With regard to all of these methods, message error checking is performed at the destination node. This requires extensive data error checking and correction transmission overhead. In addition, typically, the destination node requires circuitry for acknowledging receipt of the correct (or correctable) message.
Thus, existing network protocols, while operating reliably, tend to complicate the hardward associated with each node and/or require substantial (in relative terms) delay with respect to high priority or urgent messages.
It is therefore a primary object of the invention to maintain high communications reliability on a local area network while reducing the hardward complexity associated with network protocol. Other objects of the invention are a distributed access for each network node depending upon the priority or urgency of the message, and a correspondingly lower overhead cost per node with respect to data throughput and hardware.